Tetsuya Ogushi

Superconducting Thin Films of Bi–Pb–Sr–Ca–Cu–O by dc Magnetron Sputtering from a Single Target

Superconducting thin films of the Bi-Pb-Sr-Ca-Cu-O system have been prepared on MgO substrates by dc magnetron sputtering from a single sintered target followed by post annealing, in order to examine the effect of Pb addition. The films deposited below 600°C are always amorphous and insulating. These films crystallize by high-temperature annealing in air and become superconducting with an onset temperature of 120 K. Zero resistivity at 107 K appears when the films are deposited at 400°C and post-annealed at 850°C for 15 h. Although the superconducting properties of the films were quite sensitive to the temperature and duration of the high-temperature annealing step, the growth of the high-Tc phase in the films is clearly promoted by the addition of Pb.

Highly oriented Bi(Pb)‐Sr‐Ca‐Cu‐O superconducting thin films by magnetron sputtering of a single target

Superconducting Bi(Pb)‐Sr‐Ca‐Cu‐O thin films have been prepared onto (100) MgO substrates by dc magnetron sputtering using a single sintered target. The targets used were Bi2.7 ,Pbx Sr2 Ca2.25 Cu3.75 Oy (x=1.5, 1.75, 2.0, 2.25 and 2.5) in nominal composition. All the films were deposited at 400 °C and annealed at 850 °C for 3 h in air. Although the superconducting properties of the thin films were very sensitive to the Pb content of the target, reproducible results were obtained. After deposition from the target with x=2.0 and subsequent high‐temperature annealing, we have succeeded in obtaining highly c‐axis oriented thin films which have shown zero resistivity at 115 K. This may be due to the optimum substitution of Pb for Bi in addition to the conditions during the high‐temperature process. The average cationic ratio of the film was shown to be Bi:Pb:Sr:Ca:Cu=1.75:0.17:2:2.1:3.2 by electron‐probe x‐ray microanalysis.

As-grown superconducting thin films of Bi(Pb)-Sr-Ca-Cu-O by magnetron sputtering

As‐grown superconducting thin films of Bi(Pb)‐Sr‐Ca‐Cu‐O have been prepared on MgO (100) at 620–740 °C by dc magnetron sputtering using a single target. The as‐grown process followed by no special annealing yields c‐axis oriented superconducting thin films with a smooth surface. Although the superconducting properties of the thin films are very sensitive to the substrate temperatures during film growth, reproducible results were obtained. The c‐axis lattice constant of the films was also controlled to the values of about 24, 31, and 37 A by changing the substrate temperature. The as‐grown film deposited at 720 °C showed zero resistivity at 81 K and the critical current density increased from 8×104 A/cm2 at 77 K to 3×106 A/cm2 at 4.2 K.

Role of added fluorine to enhance the electromagnetic properties of superconducting Y-Ba-Cu-O compounds

An experimental study was carried out on the role of a small quantity of fluorine which leads to an increment of the critical current density at 77 K of an Y‐Ba‐Cu‐O compound. Such a small quantity of fluorine did not change its crystal structure according to x‐ray diffraction analysis. From the comparison of the magnetization curves of both a bulk and a powder sample, we recognized that the added fluorine plays the role of strengthening superconductive connections among the grains. To clarify the growth mechanism of those grains, we also observed the feature of the grown grains in the fluorine‐diffused sample which had an interface between Y1Ba2Cu3Oy and Y1Ba2Cu3F4Oy compounds before sintering.

Concentration Effect of Pb in Sputter-Deposited Bi-Sr-Ca-Cu-O Superconducting Thin Films

Superconducting thin films of the Pb-doped Bi-Sr-Ca-Cu-O system have been prepared on MgO substrates by dc magnetron sputtering using a single sintered target. After deposition at 400°C and post-annealing at 850°C for 3 h in air, we have succeeded in obtaining highly c-axis oriented thin films which have shown zero resistivity at 115 K. In order to examine the effect of Pb concentration, composition analysis was performed by electron probe X-ray microanalysis. As a result, the composition of the as-sputtered films deposited below 400°C was almost the same as that of the targets, except for a slight decrease in the Bi concentration. Further, we found that the Pb-content of the film decreased quickly only during the early stage of annealing at 850°C and quite slowly thereafter.

Resistance Anomaly of Nb–Si Thin Films

A resistance anomaly of very thin Nb–Si films is reported. The anomaly is characterized by a sudden drop in the resistance by a factor of ~103 at a temperature (TD) of ~180K without any application of pressure. The lower resistance-state (~zero Ω) is constant to 4.2K so far as we measured. TDdepends on measuring current and on magnetic fields. The anomaly has properties very similar to those of CuCl under high pressure.

Single Target Sputtering of As-Grown Superconducting Bi(-Pb)-Sr-Ca-Cu-O Thin Films on MgO(100)

As-grown superconducting thin films of Bi(-Pb)-Sr-Ca-Cu-O have been prepared on MgO (100) at 620–720°C by dc magnetron sputtering using a single target. The targets used were Pb-free Bi3Sr2Ca2.2Cu3Ox and Pb-doped Bi3Pb2Sr2Ca2.2Cu3Ox in nominal compositions. The as-grown process with no annealing yields c-axis oriented superconducting thin films with zero resistivity above 70 K. The superconducting properties of the thin films were affected by the substrate temperatures during film growth. The c-axis lattice constant of the films was also controlled to the value of 24–37 A by changing the substrate temperature. The best film showed zero resistivity at 76 K and a superconducting 37 A phase. The critical current density was measured at 4.2 K with Jc=2×106 A/cm2.

Change of electromagnetic properties of superconducting RBaCuO (R = Y and Er) compounds by addition of fluorine

Abstract Drastic changes of grown grains in superconducting RBaCuO (R = Y and Er) compounds were induced by an addition of a small quantity of fluorine. The addition of fluorine of 0.3–0.5 mole fraction activated the orderly growth of the grains and the resultant shape of their magnetization curves at 77 K was the desirable one, similar to that of practical superconductors used at 4.2 K.

Ultrathin film preparation of superconducting 2223 Bi(Pb)SrCaCuO by sputter deposition and rapid annealing

The growth of superconducting Bi(Pb)SrCaCuO thin films was examined. Films with various thicknesses between 100 - 3000 A were prepared on MgO(100) substrates by sputter deposition and subsequent rapid annealing. The obtained films were c-axis oriented superconducting thin films with a 2223 phase and zero resistivity at 100 - 105 K. The ultrathin film of thickness 200 A showed zero resistivity at 100 K and had a critical current density () of about at 77 K whilst in a zero magnetic field. This film displayed a of at 77 K under a 1 T magnetic field applied parallel to the film surface and perpendicular to the current direction. decreased very slightly in a low magnetic field (0 - 0.1 T) and no hysteresis was observed in the - B curve. The film also showed little degradation of in magnetic fields of up to 3 T.

Preparation of Superconducting Bi-Sr-Ca-Cu-O Thin Films by dc Magnetron Sputtering

Superconducting thin films of the Bi-Sr-Ca-Cu-O system have been prepared on MgO substrates by dc magnetron sputtering and subsequent heat treatment in order to examine the preparation conditions. The as-sputtered films deposited at substrate temperatures of about 750°C had a slightly crystalline structure and exhibited a superconducting resistive transition from 80 K to 30 K. The annealed films exhibited a superconducting resistive transition between 100 K and 80 K. Large resistivity drops at 110 K were observed when the films were deposited at relatively high substrate temperatures ranging from 650°C to 750°C and heat treated at approximately 885°C in air.